test: add unit tests for HelpWidget

[kh-ub-ayb]

Summary

This PR adds a new unit test suite for the HelpWidget class with 39 comprehensive tests covering constructor initialization, block categorization, deprecated page search, and page navigation rendering.

Changes

• Added 39 new unit tests in js/widgets/__tests__/help.test.js
• No changes to source code

Test Coverage

Describe Block	Tests	Coverage
Constructor	14	Activity ref, beginnerBlocks / advancedBlocks / appendedBlockList init as empty arrays, index = 0, isOpen = true, widget window clear / show / sendToCenter, _helpDiv creation, onclose handler (sets isOpen false, calls destroy, restores document.onkeydown), windowFor arguments, widget body maxHeight
_prepareBlockList categorization	7	Categorizes beginner blocks with helpString, categorizes advanced blocks, skips blocks without/empty helpString, appendedBlockList orders beginner first, calls _blockHelp with first block, handles empty protoBlockDict, handles mixed valid/invalid blocks
showPageByName (deprecated)	5	Finds page by name and calls _showPage, no-op for nonexistent names, finds first/last page, searches by content in any position
Page navigation logic	12	Renders content in helpBodyDiv, displays page count, known-page images without dimensions, unknown-page images with 64x64 dimensions, renders links for 4+ entry pages, no links for ≤3 entries, sets text color, calls takeFocus, disables right arrow on last page, disables left arrow on first page, enables both on middle page, clears previous content
Static properties	1	ICONSIZE = 32

Scope

• Only js/widgets/__tests__/help.test.js was added
• No changes to source code

Verification

• All 39 tests pass

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[vanshika2720]

@kh-ub-ayb Great test coverage for HelpWidget — well structured, meaningful, and CI is passing. Scope is clean (tests only)
Minor suggestion: in the future, it might be worth importing help.js directly instead of loading it via new Function(), as that would improve readability and maintainability. Not a blocker for this PR.

[kh-ub-ayb]

@walterbender @omsuneri please review